Although pericyte degeneration has been reported in eyes of diabetes and has been implicated in the pathogenesis of diabetic retinopathy, very little is known regarding the normal function of retinal pericytes, much less the pathophysiological consequences of pericyte degeneration. Recent investigations have demonstrated that pericytes in rat skeletal muscle, but not those in the heart, contract in response to perfusion of vasoactive agents, which suggests that a mechanism exists within some microvasculatures for blood flow regulation. The objectives of this research proposal are to: 1) characterize and compare pericyte ultrastructural features in retina and skin with those of skeletal muscle and heart, 2) evaluate contractile responses of pericytes in these same tissues to vasoactive agents and 3) assess effects of experimentally induced diabetes on pericyte structure and contractile responses to vasoactive agents. The approach to be used combines in vitro organ perfusion, which permits rapid switching between buffers, drugs and fixative, with electron microscopy and morphometric techniques that enable quantification of configurational changes of endothelial cells caused by pericyte contraction. The required technology is well developed and provides the only method available for quantification of pericyte (and endothelial) responses to perfused vasoactive agents in normal and diabetic tissues. The significance of this research project is that it has the potential to: 1) provide new insights into regulatory mechanisms governing microcirculatory blood flow and 2) yield new insights into the pathogenesis of diabetic microvascular disease.